1. Field of the Invention
The present invention relates to a process for the preparation of foams characterized by isocyanurate and urethane linkages, commonly known as urethane-modified polyisocyanurate foams. More particularly, the invention relates to a novel catalyst system for the preparation of these foams.
2. Prior Art
The preparation of foams characterized by isocyanurate and urethane linkages is well-known in the art. Generally, these foams are prepared by reacting an organic polyisocyanate with a polyol in the presence of a catalyst which promotes the urethane reaction and a catalyst which promotes the trimerization reaction. The foams may also be prepared by condensing in the presence of a trimerization catalyst, an isocyanate-terminated quasi-prepolymer obtained by the reaction of an organic polyisocyanate with a polyol. Several catalysts are known in the art to promote the trimerization of isocyanate groups. Examples of these catalysts are: (a) organic strong bases, (b) tertiary amine cocatalyst combinations, (c) Friedel-Crafts catalysts, (d) basic salts of carboxylic acids, (e) alkali metal oxides, alkali metal alcoholates, alkali metal phenolates, alkali metal hydroxides and alkali metal carbonates, (f) onium compounds from nitrogen, phosphorous, arsenic, antimony, sulfur and selenium, and (g) monosubstituted monocarbamic esters.
Generally, the use of the above catalysts results in formulations having short cream times, particularly, when reactive primary hydroxyl-terminated polyols are employed in the formulations. This does not lend the formulations to be of use in pour-in-place and slab stock foaming applications. It is to overcome the aforesaid shortcomings of the prior art operations that the present invention is directed.